ABSTRACT
This chapter shows how a process and instrument diagram may be of assistance, and looks at the scenario first so that those beginning a career in the instrumentation and control industry can understand the philosophy. Specification of all the required alarms, alarm messages, and the trip points at which these will initiate, is carried out during the configuration of the control blocks in the control processors. The reason for raising an alarm prior to attainment of the unwanted state is to enable safe evasive action to avoid the aftermath of being unprepared, or of finding out about the malfunction when it is too late to correct it. Most distributed control systems have alarms built in to signal the failure of any item included in the system. Modern distributed control systems, also use for their alarm systems the concept of an audible alarm, which is eventually silenced and a flashing visual that turns steady when acknowledged.
